Conversion of diacetylbenzenes to unsaturated derivatives

ABSTRACT

The use of a solvent mixture consisting essentially of from 3070 volume percent dichloromethane with the balance being chloroform, has a profound beneficial effect on the yield of the Beta , Beta &#39;&#39;-dichlorobenzenediacrolein obtained by reaction of the complex of phosgene and N,N-dimethyl-formamide with m- or pdiacetylbenzene. The diacrolein products are readily converted to the corresponding diethynylbenzenes which are useful in the making of acetylenic polymers and copolymers.

United States Patent Y Relies [45] Oct. 24, 1972 [54] CONVERSION OFPrimary Examiner-Curtis R. Davis DIACETYLBENZENES TO Attorney-James W.Underwood, Richard R.

UNSATURATED DERIVATIVES [72] Inventor: Howard M. Relles, Rexford, N.Y.

[7 3] Assignee: General Electric Company [22] Filed: Aug. 26, 1970 [21]App1.No.: 67,212

[52] U.S. Cl. ..260/668 R, 260/599 [51] Int. Cl ..C07c 15/04 [58] Fieldof Search ..260/668 R, 599

[56] References Cited UNITED STATES PATENTS 3,129,243 4/1964 Hubel..260/668 Brainard, Joseph T. Cohen, Charles T. Watts, Paul A. Frank,Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman ABSTRACT Theuse of a solvent mixture consisting essentially of from 30-70 volumepercent dichloromethane with the balance being chloroform, has aprofound beneficial effect on the yield of the B, [3'-dichlorobenzenediacrolein obtained by reaction of the complex ofphosgene and N,N-dimethyl-formamide with mor p-diacetylbenzene. Thediacrolein products are readily converted to the correspondingdiethynylbenzenes which are useful in the making of acetylenic polymersand copolymers.

6 Claims, No Drawings CONVERSION OF DIACETYLBENZENES TO UNSATURATEDDERIVATIVES The invention relates to an improvement wherein a mixture ofdichloromethane and chloroform is used as the solvent in the process forconverting diacetylbenzenes to their corresponding 13,3-dichlorobenzenediacroleins by reaction with the complex of phosgene andN,N-dimethylformamide. More particularly, this invention relates to animprovement wherein a solvent mixture, consisting essentially of from 3070 volume percent dichloromethane, the balance being chloroform, is usedin the process wherein the complex of phosgene and N,N-dimethylformamide(hereinafter designated as phosgenedimethylformamide complex) is reactedwith mdiacetylbenzene, p-diacetylbenzene or mixtures thereof to produce6,13'-dichloro-m-benzenediacrolein, B,B'diclhoro-p-benzenediacrolein, ormixtures thereof. These diacrolein products are readily converted to thecorresponding diethynyl-benzenes with an aqueous alkali metal hydroxide.unacceptable.

Polymeric acetylenes and the process for producing the same aredisclosed in U. S. Pat. No. 3,300,456 Allan S. Hay. The polymers fromdiethynylbenzenes are an extremely interesting group of polymers sincethey contain over 90 percent be 1 weight carbon. Furthermore, thediethynylbenzenes are useful in making photosensitive compositions, asdisclosed and claimed in the copending application of Allan S. Hay Ser.No. 764,287, now US. Pat. No. 3,594,175, filed Oct. 1, 1968 and assignedto the same assignee as the present invention.

Because of the wide utility for the polyacetylenic polymers as disclosedin the aforementioned patents it would be highly desirable to have aneconomical process for producing the diethynylbenzenes required asstarting materials for the polymers. Arnold et al, Coll. Czech. Chem.Comm. 24, 2385 (1959); 26, 2852 (1961) and Proc. Chem. Soc., 7, 227(1958); discussed the various reactions of carbonyl compounds with thecomplex of either phosphorus oxychloride or phosgene withN,N-dimethyl-formamide tofonn a quaternary salt which upon hydrolysis inbasic solution produces the B-chloroacrylaldehyde derivative accordingto the following equation Dialkyl ketones can react with more than onemole of the complex but an aryl alkyl keton such as acetophenone canonly react with one mole. Bodendorf et a1, Angew, Chem. (Intemat. Edit)2, 98 (1963) describes reactions of the phosphorusoxychloridedimethylformamide complex with 7. various acetophenones toproduce the corresponding B- chlorocinnamaldehydes which in the presenceof alkali gave the corresponding phenylacetylene. German Pat. No.1,213,830 describes the reaction of these complexes withdiacetyl-benzenes to produce ,B,B'- dichlorobenzenediacroleins, but doesnot describe whether or not such compounds can be hydrolyzed to thecorresponding diethynylbenzenes.

.30 volume percent dichloromethane, the balance being chloroform. Stillfurther improvements aremade in the yield, if, when hydrolyzing thequaternary salt, the reaction mixture of the diacetylbenzene andphosgene-dimethylformamide complex is added to an aqueous solution of asalt of a, strong base and weak acid, for example, sodium acetate,potassium acetate, sodium bicarbonate, potassium bicarbonate, etc. Thesalt solution should not be poured into the reaction mixture unless itcan be done almost instantaneously and with exceptionally good stirring.I have further found that the ,B,B'-dichlorobenzenediacroleins areeasily and readily hydrolyzed with aqueous alkali metal hydroxidesolutions to produce diethynylbenzenes in high yields. Because of theexcellent yields I obtain in making the diacroleins and the excellentyields on hydrolysis, the overall conversion of diacetylbenzenes todiethynylbenzenes is exceptionally high making this a very attractiveprocess for making diethynylbenaenes.

Although the dimethylformamide-phosgene complex can be preformed bybubbling phosgene into a solution of the dimethylformamide and thenadding the diacetylbenzene, the latter can be present to simplify theprocedure, since phosgene does not react with the acetyl group at roomtemperature. THe phosgene reacts with the dimethylformamide to producecarbon dioxide and the complex. The amount of phosgene that has to beadded is easily'monitored by following the evolution of carbon dioxidefrom the reaction mixture or it can be readily monitored by use of aflowmeter, noting the increase in weight of the reaction mixture or thedecrease in weight of the phosgene cylinder, etc.

One mole of phosgene reacts with one mole of dimethylformamide to formone mole of the phosgenedimethylformamide complex and one mole of carbondioxide. Theoretically, only one mole of the complex is required foreach acetyl group. However, I have found that a much faster reaction isobtained if an additional mole of the complex is used. In contrast tothe very fast reaction of the phosgene with the dimethylformamide, thereaction of the phosgene-dimethylformamide complex with thediacetylbenzene is relatively slow at room temperature but stillproceeds fast enough that it is essentially complete at room temperaturein about 12 hours. The reaction is easily monitored by nmr spectroscopyby noting the decrease of the acetyl group. If desired, the reaction canbe speeded by heating up to the reflux temperature of the mixture.

The phosgene-dimethylformamide complex is very insoluble indichloromethane but very soluble in chloroform. The quaternary saltintermediate products from the reaction of the complex with thediacetylbenzene are quite soluble in dichloromethane but relatively muchless soluble in chloroform. Although I do not want to be limited by mytheory, I believe that my high yields over that of the prior art resultbecause the mixed solvent maintains a homogeneous solution for a muchlonger period of time. The optimum ratio would be equal volumes ofdichloromethane and chloroform in the solvent composition. However,amounts as low as 30 volume percent dichloromethane up to as high as 70volume percent dichloromethane, the balance being chloroform, can beused with very effective results in increasing the yield of the reactionproducts. Even using a solvent mixture of equal parts by volume ofdichloromethane and chloroform will still result in precipitation ofsome quaternary salt intermediate product prior to completion of thereaction. After completion of the reaction, any excess phosgene ispreferably removed, for example, with a current of dry gas or byrefluxing, permitting recovery of phosgene.

In the absence of a salt of a strong base and a weak acid during theaqueous hydrolysis of the quaternary salt to the diacrolein product, themixture becomes sufficiently acidic to hydrolyze some of the diacroleinto an undesirable ketonic byproduct. The same objectionable hydrolysisreaction will occur in strongly basic solution. Therefore, it isundesirable to use a strongly basic solution to neutralize the acidformed in he hydrolysis step. By use of a salt of a strong base and aweak acid whose aqueous solution is not strongly basic, for example thealkali metal salts of alkanoic acids or bicarbonates, the hydrolysis ofthe quaternary salt is maintained essentially neutral and minimizes anyhydrolysis to undesirable byproducts. As mentioned previously it ispreferable to add the reaction mixture to a well stirred aqueoussolution of the salt of a strong base and a weak acid. Because they arereadily available and low in cost, the preferred salt is sodium acetateor sodium bicarbonate. During the hydrolysis reaction, the reactionmixture, which is added as a slurry, becomes a clear organic layer. Itis separated from the aqueous layer, washed with water and dried.Removal of the solvent leaves. the desired,B,fldichlorobenzenediacrolein as a white crystalline solid which can befurther purified if desired by recrystallization.

The diacrolein product is readily converted to the desireddiethynylbenzene by reaction with an alkaline aqueous solutionpreferably an aqueous solution of an alkali metal hydroxide, for examplesodium hydroxide, potassium hydroxide, lithium hydroxide, rubidiumhydroxide, cesium hydroxide, etc. Because of its cheapness and readyavailability, sodium hydroxide is preferred. The reaction will proceedat room temperature but is greatly hastened by heating in thetemperature range of 50 C. up to the reflux temperature. The reaction isgreatly hastened by using a solvent combination in which both the alkaliand the chlorinated diacrolein are soluble. A mixture of dioxane andwater is ideal for this purpose.

The diethynylbenzene is isolated by adding additional water andchloroform to the reaction mixture, acidifying with hydrochloric acid,and separating the chloroform solution which is washed with water toremove traces of dioxane and dried with a desiccant, for example,anhydrous magnesium sulphate. The diethynylbenzene is isolated byevaporation of the chloroform.

In order that those skilled in the art may better understand myinvention, the following examples are given by way of illustration andnot by way of limitation.

EXAMPLE 1 A solution of 8.1 l g. of m-diacetylbenzene and 14.62 g. ofN,N-dimethylformamide in 50 ml. of dichloromethane and 50 ml. ofchloroform was put in a 300 ml. round-bottomed flask, cooled with a coldwater bath and equipped with astirrer, thermometer, and a refluxcondenser having a drying tube at the top. Phosgene was introduced at arelatively slow'rate' for the first 8 minutes during which time anexothermic reaction with vigorous evolution of carbon dioxide occurred.The flow rate of the phosgene was increased to approximately four gramsper minute during the next 7 minutes by which time the evolution ofcarbon dioxide had become very slow indicating essentially completeconversion of the dimethylformarnide to the dimethylformamideOphosgenefrom complex The flow of phosgene was stopped and the reaction allowedto proceed at ambient temperature.

In five minutes the solution was turbid and in 2% hours a precipitatehad formed in such large quantity that the solution was very stiff andhard to stir. An additional 50 ml. of chloroform and 50 ml. ,ofdichloromethane was added and the reaction allowed to proceed at ambienttemperature for an additional 13 hours. Under vigorous stirring toinsure a representative sample, a sample was withdrawn and hydrolyzedwith an excess of 20 percent by weight aqueous sodium acetate solution,the organic layer separated, washed well with water and dried. At thispoint, analysis by vapor phase chromatography showed the reactionmixture to be 96 percent ,B,'B-dichlorobenzenediacrolein and 4 percentdiacetylbenzene. After an additional 25 hours reaction, analysis byvapor phase chromatography of a sample taken as described above showedno evidence of the presence of diacetylb'enzene.

The excess phosgene and solvent were removed with a stream of drynitrogen passing through the reaction mixture overnight. The solidresidue was slurried with 100 ml. of chloroform and added to 250 g. of a20 percent by weight aqueous sodium acetate solution with rapid stirringwhich caused all of the solid to disappear leaving two liquid phases.The organic phase was washed with three 100 ml. portions of water anddried over anhydrous magnesium sulphate. After filtering the dryingagent from the solution, the solvent was evaporated under vacuum leaving12.46 g. of a white solid which is 97.5 percent of theory forI3,B-dichlorom-benzenediacrolein. This product was analyzed by nmrspectroscopy and vapor phase chromatography and found to be greater thanpercent pure. It was further purified by recrystallization from acetone.

When Example 1 is repeated but p-diacetylbenzene is used in place of them-diacetylbenzene, the product is 3,6-dichloro-p-benzenediacrolein.

EXAMPLE 2 A solution of 0.50 g. of fl,B'-dichloro-m-benzene diacroleinfrom Example 1 in 10 m1. of dioxane was added dropwise during 10 minutesto 10 ml. of a 10 percent aqueous solution of sodium hydroxide and 10ml. of dioxane at 80- 82 C. with rapid stirring. After refluxing for 25minutes, the reaction mixture was added to 100 ml. of water and 100 ml.of chloroform and the aqueous layer acidified with 2.5 ml. ofconcentrated aqueous hydrochloric acid. After vigorous shaking, thechloroform layer was separated and dried over anhydrous magnesiumsulphate. Analysis of the solution by vapor phase chromatography showedthat the product was greater than 98 percent m-diethynylbenzene withless than 2 percent of two unidentified impurities. Them-diethynyl-benzene was separated form the solvents by carefulevaporation of the solvents under vacuum care being taken to preventloss of the m-diethynylbenzene which has a relatively high vaporpressure at room temperature. Alternatively, the mdiethynylbenzene canbe separated by fractional distillation, care being taken to preventpolymerization of the product.

When Example 2 is repeated but B,B'-dichloro-pbenzenediacrolein is usedin place of the B,B-dichlorom-benzenediacrolein, the product isp-diethynylbenzene.

As will be readily apparent to those skilled in the an, mixtures of thevarious diacetylbenzenes can be converted into the corresponding B,,B'-dichlorobenzenediacroleins and these diacroleins can be converted intothe corresponding diethynylbenzenes. Although the above examples haveillustrated the preferred embodiments of my invention, variousmodifications within the scope of the invention will be readily apparentto those skilled in the art and are within the scope of the invention asdefined in the appended claims.

What I desire to secure by Letters Patent of the United States is:

1. In the process of making B,B'-dichloro-mbenzenediacrolein,[3,,8'-dich1oro-p-benzenediacrolein or mixtures thereof by reactingm-diacetylbenzene, pdiacetyl-benzene or mixtures thereof with thecomplex of phosgene and N,N-dimethylformamide, the improvement whereinthe reaction is carried out in a solvent mixture consisting essentiallyof from 30 volume percent dichloromethane, the balance being chloroform.

2. The process of making m-diethynylbenzene, pdiethynylbenzene ormixtures thereof which comprises making,B,B'-dichloro-m-benzenediacrolein, 3,3- dichloro-p-benzenediacrolein ormixtures thereof by the process of claim 1 and thereafter reacting saidbenzenediacrolein with an aqueous alkali metal hydroxide to convert itto the corresponding diethynylbenzene.

3. The process of claim 1 wherein B,B-dichloro-mbenzenediacrolein ismade from m-diacetylbenzene.

4. The process of claim 1 wherein ,B,,B-dichloro-pbenzenediacrolein ismade form p-diacetylbenzene.

5. A process of claim 2 wherein m-diethynylbenzene is made fromm-diacetylbenzene.

6. The process of claim 2 wherein p-diethynylbenzene is made fromp-diacetylbenzene.

2. The process of making m-diethynylbenzene, p-diethynylbenzene ormixtures thereof which comprises making Beta , Beta''-dichloro-m-benzenediacrolein, Beta , Beta''-dichloro-p-benzenediacrolein or mixtures thereof by the process ofclaim 1 and thereafter reacting said benzenediacrolein with an aqueousalkali metal hydroxide to convert it to the correspondingdiethynylbenzene.
 3. The process of claim 1 wherein Beta , Beta''-dichloro-m-benzenediacrolein is made from m-diacetylbenzene.
 4. Theprocess of claim 1 wherein Beta , Beta ''-dichloro-p-benzenediacroleinis made form p-diacetylbenzene.
 5. A process of claim 2 whereinm-diethynylbenzene is made from m-diacetylbenzene.
 6. The process ofclaim 2 wherein p-diethynyl-benzene is made from p-diacetylbenzene.